Industrial Vapour Generator For Depositing An Alloy Coating On A Metal Strip

ABSTRACT

The present invention relates to a vacuum deposition facility for depositing a metal alloy coating on a substrate ( 7 ), said facility being equipped with a vapour generator/mixer comprising a vacuum chamber ( 6 ) in the form of an enclosure provided with means for creating a vacuum state therein relative to the external environment and provided with means for the entry and exit of the substrate ( 7 ), while still being essentially sealed from the external environment, said enclosure including a vapour deposition head, called the injector ( 3 ), configured so as to create a jet of metal alloy vapour of sonic velocity towards the surface of the substrate ( 7 ) and perpendicular thereto, said ejector ( 3 ) being in sealed communication with a separate mixer device ( 14 ), which is itself connected upstream to at least two crucibles ( 11, 12 ) respectively, these containing different metals M 1  and M 2  in liquid form, each crucible ( 11, 12 ) being connected to the mixer ( 14 ) by its own pipe ( 4, 4 ′).

FIELD OF THE INVENTION

The present invention relates to an industrial vapor generator forcontinuously vacuum coating a substrate in motion, more particularly ametal strip, using metallic vapors in order to form a layer of metalalloy on its surface, so as to give it excellent resistance to corrosionwhile preserving good drawing and weldability characteristics.

BACKGROUND OF THE INVENTION

It has been known since the late 1980s that the deposition of certainalloys, such as ZnMg, on the surface of a steel strip plays a role inprotecting steel. The excellent corrosion resistance of the ZnMg alloyis attributed to the nature of the corrosion products formed on thesurface of the strip in an extremely dense layer acting as a barrierfilm.

Such an alloy deposition is generally only possible by the usualtechniques, such as electrolytic deposition, hot dipping, etc., withincertain composition limits. Thus, at atmospheric pressure, contaminationof the liquid metal bath by the oxygen in the air may occur, which formsoxide mattes on the surface of the bath.

If one wishes to obtain extended thickness and composition ranges, theonly possible solution is often the vacuum evaporation of the liquidmetal, pure or in alloy form (PVD technique, Pressure Vapor Deposition).

In the context of this technique, it is known to place the substrate ina vacuum enclosure maintained at a low temperature and comprising acrucible of molten metal. The deposition is then achieved on all thewalls with a temperature below the temperature of the metal vapor. Toincrease the deposition yield on the substrate and prevent waste, it istherefore interesting to heat the walls of the enclosure.

In document WO-A-97/47782, a method is described for continuouslycoating a moving substrate in which the metal vapor is generated byinduction heating a crucible containing a bath formed by the coatingmetal in a vacuum enclosure. The vapor escapes from the crucible via apipe that brings it towards an outlet orifice, preferably calibrated, soas to form a jet oriented towards the surface of the substrate to becoated. The use of an orifice in the form of a longitudinal slot with anarrow section allows to regulate the vapor mass flow rate, at constantsonic velocity along the slot (sonic throat), which procures theadvantage of obtaining a uniform deposition. This technique willhenceforth be designated using the acronym “JVD” (Jet Vapor Deposition).

This technology does, however, have several flaws, in particular:

-   -   the constant supply of liquid metal involves providing its        return to the vat in one or several points;    -   the liquid metal comprising impurities, there is a concentration        of these impurities on the surface of the bath after        evaporation, which reduces the flow rate. The uniformity of the        bath is necessary to obtain a uniform deposition. It involves        bringing cool liquid at a location whilst removing the used        liquid at another location. One solution would be skimming the        surface or recycling the load, but any mechanical operation is        made difficult in a vacuum;    -   the difficulty of adapting the evaporation slot to a variable        bandwidth, which involves concealing means on either side of the        slot, and hence the production of vapor sealing under vacuum and        at 700° C., which is not easy to do;    -   the difficulty of concealing the slot when the movement of the        strip is interrupted, which would involve the presence of a        sealing linear valve over a typical length of 2 meters or more;    -   the major thermal inertia of the system (at least several        minutes);    -   the heating, done by vacuum induction, requires passing all of        the electrical heating power via electrical connectors through        the vacuum sealing wall, which does not facilitate the        accessibility and maintainability of the facility.

Furthermore, the state of the art does not provide a satisfactorysolution to the need to perform the co-deposition of two distinctmetals, involving the mixture of two jets leaving the evaporator. Theuse of intermediate mixing boxes with baffles did not provide asufficiently convincing result.

A first way to proceed for depositing an alloy coating on a strip is tofirst deposit a layer of the first metal, such as zinc, for example byhot dipping, electrolysis or vacuum magnetron spraying, then deposit alayer of a second metal, such as aluminum, for example in a vacuum, andto finally perform a thermal diffusion treatment, for example lowtemperature annealing, which produces the alloy.

The advantage of this method is that it has a simple design, allowingfor a step by step regulation.

A first drawback is, however, multiplying the steps of the method, andtherefore its cost. In particular, thermal diffusion treatment consumesa significant amount of energy. For example, if the relative thicknessof the coating is 1%, the required energy must be provided to the entirethickness of the finished product, i.e. 100%, which corresponds toseveral megawatts for an industrial line.

Thus, document WO-A-02/14573 describes the development of a coating froma base zinc plated coating obtained by a conventional hot dipping orelectro-galvanizing method, which in turn is then vacuum coated withmagnesium. Rapid induction heating allows to postpone the fusiondeposition for several seconds and to obtain, after cooling, a favorablemicrostructural distribution of alloyed phase ZnMg in the entirethickness of the layer.

Document FR 2 843 130 A describes a method for coating a surface with ametal material, according to which:

-   -   a first coating of said material is achieved using a metal or        metal alloy layer,    -   a thermal treatment is achieved on the first coating using a        rapid heating means so as to bring the surface of said first        coating to a temperature below the melting temperature of the        metal material, and    -   a second coating is deposited from a metal or metal alloy.

The Applicant has also proposed an industrial dual-layerelectro-galvanized/ZnMg alloy product obtained by PVD (EP-A-0 756 022),as well as an improvement of the method with an infrared heating systemto alloy the magnesium with the zinc in order to minimize the formationof the fragile intermetallic FeZn phase.

A second drawback is that not all types of steel accept this thermaltreatment. For example, BH (bake hardening) steels are malleable,deformable, anti-corrosion steels intended for automobiles, which haveinstabilities that are displaced during curing of the paint, whichcauses the sheet metal to harden. This product therefore has adifficulty related to hardening that results from its reheating. Adirect alloy deposition would therefore allow to overcome thesedrawbacks.

Another method is therefore to produce metal coating alloys by directdeposition of the alloy without thermal treatment, by rigorouslycontrolling the concentration of both metals in the crucible. Forexample, if 50% Zn and 50% Mg are placed in the crucible, an alloy of85% Zn/15% Mg is obtained, given the different evaporation speeds.However, this control involves great difficulties in managing thesystem, in light of the continuous concentration variation in thecrucible. In particular, it is difficult to ensure homogeneity in thecrucible, especially if it is not of circular section. For example,POSCO (publication: “Next Generation Automotive Steels at POSCO,”January 2008) proposes a coating obtained by PVD at very high velocity,with a high vapor yield and high energy yield, in particular in the formof an alloy co-deposition from a single evaporation source.

Still another method according to the state of the art consists in usingtwo crucibles, each generating a type of vapor, both generated vaporsbeing oriented by a channel towards a mixing device, from which thealloy is deposited on the strip.

Patent BE 1010720 A3 describes a method for continuously coating asubstrate in motion using a metallic alloy in vapor phase, in which thevarious components of the alloy are evaporated into suitable distinctelements and whereof the different metal vapors obtained are channeledtowards the location where the deposition occurs.

One of the vapors coming from the metal baths with the components of themetal alloy plays the role of a propellant element relative to the othermetal vapors present.

In document WO-A-02/06558, a ZnMg coating is obtained in a vacuum byevaporating from two crucibles, one with zinc and the other withmagnesium. Before they are projected on the strip, the vapors are mixedin a throttling device in the form of plates provided with holes orslots, which allows to obtain maximum sonic velocity and vapor flowrate. However, the high speed of the vapors before mixing makes it verydifficult to obtain a homogenous mixture by molecular diffusion.

In L. Baptiste et al., “Electromagnetic levitation: A new technology forhigh rate physical vapour deposition of coatings onto metallic strip”,Surface & Coatings Technology 202 (2007), 1189-1193, a method isproposed based on the levitation technology for conductive materials inhigh-frequency electromagnetic fields. Through a suitable design of theinduction coils, it is possible to obtain high power densities andmetals at low vapor pressures such as aluminum, nickel, or copper, aswell as their alloys can easily be evaporated. The produced vapor isguided towards the substrate by a specially designed vapor distributionsystem, which allows to obtain good uniformity of the coating and verywide use of the vapor.

Document U.S. Pat. No. 5,002,837 describes the evaporation deposition ofa dual-layer Zn/ZnMg coating with a completely alloyed Zn₂Mg orZn₂Mg/Zn₁₁Mg₂ phase.

Patent application EP-A-2 048 261, in the name of the Applicant,discloses a vapor generator for depositing a metal coating on a steelstrip, comprising a vacuum chamber in the form of an enclosure, providedwith means for ensuring a vacuum state therein relative to the outsideenvironment and provided with means allowing the strip to enter andexit, while being essentially sealed relative to the outsideenvironment. This enclosure covers a vapor deposition head, calledejector, configured to create a metallic vapor jet at sonic velocitytowards and perpendicular to the surface of the strip. The ejector is insealed communication via a supply duct with at least one cruciblecontaining a coating metal in liquid form and situated outside thevacuum chamber. The vapor generator comprises means for regulating theflow rate, pressure, and/or speed of the metallic vapor in the ejector.Document EP-A-2 048 261 belongs to the state of the art pursuant toArticle 54(3) EPC.

Prior patent application EP-A-1 972 699, in the name of the Applicant,discloses a method and facility for coating a substrate according towhich a layer of metallic alloy comprising at least two metal elementsis continuously deposited on said substrate, using the vacuum depositionfacility comprising a vapor jet coating device, allowing to project onthe substrate a vapor comprising the metallic elements in apredetermined relative and constant proportion, the vapor being broughtto sonic velocity beforehand. The method is more particularly intendedfor the deposition of ZnMg coatings.

AIMS OF THE INVENTION

The present invention aims to provide a solution that allows to overcomethe drawbacks of the state of the art.

In particular, the invention aims to achieve the following objectives:

-   -   no liquid source in the vacuum enclosure for deposition;    -   ease of production;    -   very significant reduction in the mixing length of two or more        metallic vapors;    -   possibility of very fast differentiated and adjustable        regulation of the individual alloy metal content levels;    -   easy accessibility and maintenance of the crucible(s);    -   excellent uniformity of the evaporation and mechanism simple for        adaptation on strip widths that can exceed 2 meters;    -   maximized vapor flow rate;    -   easy regulation of the vapor flow rate, by controlling the        electrical power and/or temperature of the evaporation surface;    -   design of a very flexible facility for alloy depositions        entirely in vacuum.

MAIN CHARACTERISTIC ELEMENTS OF THE INVENTION

A first object of the present invention relates to a facility fordepositing under vacuum a metal alloy coating on a substrate, preferablya metal strip in continuous motion, equipped with a vaporgenerator-mixer comprising a vacuum chamber in the form of an enclosure,provided with means for ensuring a vacuum state therein relative to theexternal environment and provided with means for the inlet and outlet ofthe substrate, while being essentially sealed relative to the externalenvironment, said enclosure comprising a vapor deposition head, calledthe ejector, configured so as to create a jet of metal alloy vapor atsonic velocity towards the surface of the substrate and perpendicularthereto, said ejector being in sealed communication with a separatemixer device, which is itself connected upstream to at least twocrucibles, respectively, and containing different metals M1 and M2 inliquid form, each crucible being connected to the mixer by its own pipe.

According to preferred embodiments of the facility for depositing undervacuum a metal alloy coating on a substrate according to the presentinvention, the latter also comprises one or more of the followingfeatures in combination with the basic features of the facility:

-   -   the mixer comprises a cylindrical envelope inside which, along        the axis of the envelope, are located a plurality of tubes,        arranged regularly and connected at the inlet to the supply pipe        of a first metal vapor, the supply pipe of a second metal vapor        being connected, laterally relative to the cylindrical envelope,        to the interstitial space between the tubes. The tubes and the        interstitial space having outlet orifices all emerging on a        space where the mixing of the vapors can occur;    -   the mixer comprises a series of partitions allowing to separate        at least two entering vapors, these partitions creating orifices        allowing the two vapors to exit before they are mixed in the        form of alternating layers of both vapors in the direction of        the exiting flow;    -   each of said pipes comprises a proportional valve, optionally        with a head loss device;    -   the proportional valve is of the butterfly valve type;    -   the ejector comprises a longitudinal exit slot for the vapor,        acting as a sonic throat, extending over the entire width of the        substrate and a filtering medium or a head loss member made of        sintered material, preferably made of titanium or in the form of        a metal sieve with sintered stainless steel fibers, so as to        equalize and rectify the velocity vectors of the vapor leaving        the ejector;    -   the facility comprises means for adjusting the length of the        slot to the width of the substrate;    -   said means comprise a means for rotating the ejector around its        supply pipe;    -   the ejector, the mixer, the pipes and the crucibles are        thermally isolated from the outside environment and heated by a        radiation heater;    -   the facility comprises optional heating means for the vacuum        enclosure;    -   a first porous surface is arranged at the outlet of the mixer        tubes and/or a second porous surface is arranged at the outlet        of the interstitial space of the mixer, so as to balance the        pressures of the two respective vapors;    -   an additional pipe is mounted in bypass on the supply pipe of        the first metal M1 towards the mixer, having an isolating valve        and leading to an additional ejector in the vacuum chamber, said        additional ejector being configured to create a vapor jet of the        first metal M1 at sonic velocity towards and perpendicular to        the surface of the substrate, the portion of the supply pipe of        the first metal M1 leading to the mixer being provided with an        additional valve intended to isolate the first crucible from the        mixer.

A second object of the present invention relates to a method fordepositing a metal alloy coating on a substrate, preferably a metalstrip in continuous motion, using the facility described above, wherein:

-   -   the flow velocity of each of the metal vapors is regulated at        the inlet of the mixer so that said flow velocity of said vapors        at the inlet of the mixer is lower by a factor of 10, preferably        by a factor of 50, than sonic velocity;    -   the concentration of each metal is independently adjusted during        the mixture of the vapors to be deposited on the substrate.

Advantageously, the method is implemented so that the flow velocity isless than 100 m/s, preferably from 5 to 50 m/s.

Still advantageously, according to the method of the invention forimplementing the above-mentioned facility for depositing under vacuum ametal alloy coating on a substrate, preferably a metal strip incontinuous motion, said additional valve being closed and said isolationvalve being open, the first metal M1 may be deposited on the substrateat the level of the additional ejector and the second metal M2 may bedeposited at the level of the ejector in the vacuum chamber,successively.

Still advantageously, according to the method for implementing theabove-mentioned facility for depositing under vacuum a metal alloycoating on a substrate, preferably a metal strip in continuous motion,said additional valve being open and said isolating valve being closed,the M1+M2 alloy is directly deposited on the substrate at the level ofthe ejector in the vacuum chamber.

Still advantageously, according to the method for implementing theafore-mentioned facility for the depositing under vacuum a metal alloycoating on a substrate, preferably a metal strip in continuous motion,both the additional valve and the isolating valve being open, the firstmetal M1 is deposited on the substrate at the level of the additionalejector and the M1+M2 alloy is directly deposited at the level of theejector in the vacuum chamber, successively.

Advantageously, according to the afore-mentioned methods, the metal oralloy deposition(s) are followed by a thermal treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically shows a vapor generator with a mixer accordingto the invention, which allows an alloy deposition of two pure metals onthe substrate.

FIGS. 2A to 2C show detailed views of the metal vapor mixer according toone preferred embodiment of the present invention.

FIGS. 3A and 3B diagrammatically show a planar view and an elevationview, respectively, of a complete bimodal facility according to onepreferred embodiment of the present invention, which can be used eitherfor the deposition of two distinct metal species on a metal strip, orfor a direct alloy deposition using the aforementioned mixer.

FIG. 4 shows more perspective views of the pipes of the facilityaccording to FIGS. 3A and 3B.

FIG. 5 shows the analysis results of a ZnMg coating by glow dischargeoptical emission spectroscopy (GDOES) during implementation tests of theinvention on a pilot line, expressed in zinc and magnesium weight (in %of the targeted nominal values, I/In), obtained at various points overthe entire width of the coated strip.

FIG. 6 shows the composition of an alloy of the ZnMg type as well as theevolution of the layer weight obtained as of the moment when the valvesof the JVD facility are open (ICP analysis along the strip).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The solution recommended according to the present invention consists inusing an offboard evaporation crucible, i.e. that is dissociated from aJVD evaporation head with a longitudinal slot or calibrated holes forthe vapor outlet, herein after called ejector. The general principle ofsuch an offboard crucible device, in the case of a single vapor speciesto be deposited, is described in detail in patent application EP-A-2 048261.

The present patent application is based on the deposition of an alloycoating and therefore requires at least the use of two different sourcesof metal vapor.

In the case where one wishes to mix the vapors of two different coatingmetals, as shown in FIG. 1, two melting chambers or crucibles 11,12containing two different pure metals (for example, zinc and magnesium,)respectively, are each connected by a pipe 4,4′ provided with a valve5,5′ to a mixing chamber 14 coupled to the ejector 3. The concentrationof both metals in the mixture is adjusted on one hand using the energysupplied and on the other hand using respective proportional valves5,5′, which simplifies the management problem. The bulk of this systemis advantageously reduced (see below).

Owing to the present valves, this device allows to finely and quicklyregulate the vapor flow. In this respect, the choice of cylindricalpipes allows to obtain a good high-temperature vacuum sealing and theuse of a proportional valve 5, for example a butterfly valve ascommercially available, possibly with a head loss device 5A, to regulatethe vapor flow rate. The deposited thickness depends on the metal vaporflow rate, the flow rate itself being proportional to the useful powersupplied. When the power is modified, it is possible to simultaneouslychange the position of the valve in order to adapt the head loss to thenew operating point. The mass flow rates also change instantaneously,which makes transients practically nonexistent during the change ofposition of the valve.

The ejector 3 is a box with a length greater than the width of the stripto be coated. This device comprises a filtering medium or a mediumcreating a head loss (not shown) to ensure the equalization of the vaporflow rate over the entire length of the box. The ejector 3 is heated toa temperature above that of the metal vapor and is thermally insulatedon the outside. A calibrated slot or a series of holes ensure theprojection, at the speed of sound, of the metal vapor on the strip 7.Depending on the density of the metal, the velocities obtained typicallyrange from 500 to 800 m/s. The sonic throat over the entire length ofthe slot very effectively completes the filtering medium to ensure theuniformity of the deposition on the strip. The size of the slot or holesS imposes the volume flow rate (k×v_(son)×S, k˜0, 8). The speed ofsound, v_(sound), is reached in the ejector at the outlet of the slot orholes. Owing to the presence of a head loss element in the pipe (valve5), the vapor flow rate may be regulated and imparted with a low initialpressure.

In the state of the art (see WO-A-02/06558), the two supply pipes of theejector are provided with restrictions in the form of calibratedorifices. It is then in that location that the speed of sound isobtained (several hundreds of m/s). If a mixing time t0 is necessary toobtain perfect mixing, then if the vapors have a speed v0 at the outletof these calibrated holes, the mixing member should have a length v0×t0.For example, if v0=500 m/s and t0=0, 2 s, then v0×t0=100 m ! As aresult, with such a principle, the mixture actually deposited is hencenever perfect. This results in homogeneity problems with the coating.

However, the device according to the invention, described in FIG. 1,allows to mix the vapors this time at a low speed owing to the head losselements incorporated into the system such as valves. The mixing is donebetween vapors having regulated flow velocities and typically between 5and 50 m/s at the inlet of the mixer (these flow velocities thereforebeing lower by at least a factor of 10, preferably by a factor of 50,than sonic velocity), which allows to reduce the homogeneity length by afactor ranging from 10 to 100 (therefore typically several meters).

For example, tests done on the Applicant's JVD pilot line allowed toproduce coatings having magnesium content levels between 0 wt % and 15.6wt %.

It was possible to validate the partial magnesium and zinc pressuresowing to these tests from chemical analyses done on the producedcoatings. The pressures obtained in the zinc crucible were between 1956Pa and 8736 Pa, whereas those obtained in the magnesium crucible werebetween 241 Pa and 1467 Pa.

The total pressures (Zn+Mg) in the mixer obtained during these sametests were between 241 Pa and 1440 Pa. The velocities of the metalvapors in the mixer calculated from this experimental data are between9.81 m/s and 22.7 m/s, or between 0.02 and 0.04 Mach (therefore muchlower than the speed of sound).

Furthermore, the same chemical analyses demonstrated that the mixing ofvapors achieved with a facility as described in this invention allowedto perform depositions having a uniform composition over the entirewidth of the strip. FIG. 5 shows, as an example, the zinc and magnesiumweights (expressed in percentage of the targeted nominal values)obtained by analysis at various points over the entire width of thestrip coated using this method.

Lastly, FIG. 6 shows the evolution of the composition of a standardalloy as well as the evolution of the weight of the obtained layer as ofthe moment when the valves of the JVD facility are open. In fact, thisextreme example demonstrates that the system established according tothis invention allows to manage the transients of an industrial line(stop, speed change, format change, etc.), since the desired target isobtained as soon as the valves are opened and remains stable all throughthe rest of the production campaign.

Furthermore, in the case of mixers, the principle of increasing themolecular diffusion is known if several layers of two gases A and B arealternatingly put in contact, rather than a layer of A and a layer of B.The number of separating walls in the diffuser allows to furthersubstantially reduce the diffusion length and the mixing time. Theapplication of this principle in a mixer of the type described aboveallows to reduce the mixing length to a few centimeters, and thereforeto design a smaller mixer, which is an advantage given the complexity ofthe system (vacuum ejector, high temperature).

The feasibility of such a mixer working with metal vapors at lowvelocity and alternative distribution was studied by digital simulation.The result led to the design of a preferred embodiment according to theinvention, shown in FIGS. 2A to 2C.

According to this preferred embodiment, the mixing device 14 is in theform of a cylindrical envelope 14C whereof the inside comprises aplurality of tubes 14A arranged regularly and connected to the supplypipe 4′ of a first metal vapor M1, along the axis of said cylinder. Thesupply pipe 4 of the second metal vapor M2 is connected, laterally tothe cylindrical envelope, to the interstitial space 14B located insidesaid cylindrical envelope 14C, between the tubes 14A. The tubes 14A aremaintained and fastened on a flange 16. Both the tubes 14A and theinterstitial space 14B all emerge at the outlet on the mixing spacestrictly speaking 15.

The choice of a cylindrical symmetry for the design of the mixing deviceis of course related to its good pressure resistance.

The use of an offboard low-speed system, owing to outer adjustmentvalves, with a vapor mixer has certain advantages over theco-evaporation known from the state of the art. It is in fact mucheasier to adjust the vapor content required for each metal owing to thecombined action of the power and the respective individual valves oneach vapor. The power allows to adjust the mixed quantities and thevalves allow to quickly set and modify the operating point. It is infact possible, owing to the head loss of the valve, to vary the pressurewithout modifying the temperature behind the valve. Conversely,according to the state of the art, the pressure modification is alwayssubject to the temperature variation, therefore to the heating, andgenerates inertia and transients.

The required pressure is different for the two metals M1 and M2 (e.g.T_(evap)(Zn)=600° C. and T_(evap)(Mg)=700° C.) because they do not havethe same density or physical characteristics.

Under these conditions, it is possible to balance the differentpressures of the two respective gases by adding to the circuit twoadditional head loss elements in the form of porous surfaces (notshown). A first porous surface is arranged at the outlet of the tubes14A (metal M1) and a second porous surface is arranged at the outlet ofthe interstitial gas (metal M2). In this case, the re-equalizing of thepressures or of the speeds is achieved by friction, i.e. by heattransfer, and the adiabatic expansion of the gas (without heat transfer)that would lead to recondensation is thereby avoided.

The advantage of the invention in this respect is to be able to managegases with different temperatures or pressures at the inlet, since headlosses are used in the form of valves that allow, in combination withthe energy source, to adjust the content levels of the two metal vapors.

Another object of the invention is to propose a “bimodal” vacuumdeposition facility, shown in FIGS. 3A, 3B and 4, which allows thefollow deposition forms:

-   -   deposition of M1, then of M2, both depositions being in a        vacuum,    -   deposition of M1+M2, in the form of a mixing achieved as        described above, the alloy deposition being in a vacuum;    -   deposition of M1+(M1+M2), in the form of a mixing achieved as        described above, the complex alloy deposition being in a vacuum.

As shown in the figures, the part of the facility that provides themetal M2 from the crucible 11 is provided with a mixer 14. The facilitycan operate independently for the deposition of M1 on the metal strip atthe level of the ejector 3′ in the vacuum chamber 6, if M1 is not mixedwith M2, i.e. if a valve 5B is closed in the portion of the pipe 4′conveying M1 in the mixer (when this valve 5B is open). Likewise, in thecase where this valve 5B is closed, the portion of the facilitysupplying M2 from the crucible 11 can operate autonomously and allow thedeposition of M2 in the vacuum chamber 6, for example above the layer ofM1 already deposited (for a left-to-right travel direction of the stripin FIG. 3A). However, if the aforementioned valve 5B is open, the mixingM1+M2 will be achieved in the mixer 14 and deposited on the strip at thelevel of the ejector 3 in the vacuum chamber 6. Other alloy depositionpossibilities can be considered with this facility such as a depositionof M1 at the level of the ejector 3′ followed by a later deposition ofthe mixture M1+M2 at the level of the ejector 3. It can in fact beadvantageous to perform a deposition of zinc and magnesium alloy on asub-layer of zinc, which is relatively ductile, in order to preventchalking of the coating.

In FIG. 3A, the proportional valves (5,5′) were lined by valves (5C,5C′)at the outlet of the respective crucibles.

The present invention fits into a context of evolution of the technicalfield that approaches “full PVD” for the following reasons:

-   -   in electrolytic deposition, the increase of the strip velocity        involves the increase of the required currents (millions of        amperes) and therefore of the consumption (megawatts), which is        prohibitive in terms of energy consumption; furthermore, this        technology creates spatters, which limits the maximum strip        velocity to about 160 meters/minute;    -   hot dipping for the deposition of a first layer of zinc        encounters the physical limitation related to centrifuging, the        effectiveness of which decreases at high velocity; the        admissible strip velocity limit is about 180 meters/minute;    -   in the case of vacuum deposition, this limit of 160-180        meters/minute disappears because a damaging liquid phase is no        longer present. The metal vapors are at the speed of sound in        the deposition enclosure and there is therefore no longer any        chemical, electrical or physical limitation. In the future, we        can hope to reach 200-220, or even 300 meters/minute, owing to        the technology of the invention.

ADVANTAGES OF THE INVENTION

The system according to the invention allows to obtain a very gooduniformity of the temperature and velocity of the deposited vapor, whilebeing reliable and accessible and having very low response times. Theinvention thus meets the requirements for industrialization of themethod very well.

Furthermore, the offboard device according to the invention isparticularly suited to alloy deposition by vapor mixing because itallows to adjust the deposited chemical composition without having tomodify the composition of a liquid alloy. The vapor mixing is thusachieved in a pipe at very low flow velocity, unlike the state of theart.

Another significant advantage is allowing, using the mixer of theaforementioned type, to obtain a mixing length at values as low as300-600 mm, this advantage being particularly decisive in light of thenecessary bulk reduction, knowing that such a device should be kept in avacuum at a temperature of about 750° C.

1-19. (canceled)
 20. A facility for depositing under vacuum a metalalloy coating on a substrate (7), equipped with a vapor generator-mixercomprising a vacuum chamber (6) in the form of an enclosure, providedwith means for ensuring a vacuum state therein relative to the externalenvironment and provided with means for the inlet and outlet of thesubstrate (7), while still being essentially sealed relative to theexternal environment, said enclosure including a vapor deposition head,called ejector (3), configured so as to create a jet of metal alloyvapor at sonic velocity towards the surface of the substrate (7) andperpendicular thereto, said ejector (3) being in sealed communicationwith a separate mixer device (14), which is itself connected upstream toat least two crucibles (11,12), respectively, and comprising differentmetals M1 and M2 in liquid form, each crucible (11,12) being connectedto the mixer (14) by its own pipe (4,4′), wherein the mixer (14)comprises a series of partitions allowing to separate at least twoentering vapors, these partitions creating orifices allowing the twovapors to exit so as to be mixed in the form of alternating layers ofboth vapors in the direction of the exiting flow.
 21. The facilityaccording to claim 20, wherein the mixer (14) comprises a cylindricalenvelope (14C) inside which, along the axis of the envelope, are locateda plurality of tubes (14A) arranged regularly and connected at the inletto the supply pipe (4) of a first metal vapor, the supply pipe (4′) of asecond metal vapor being connected, laterally relative to thecylindrical envelope, to the interstitial space (14B) between the tubes(14A), the tubes (14A) and the interstitial space (14B) having outletorifices all emerging on a space (15) where the mixing of the vapors canoccur.
 22. The facility according to claim 20, wherein each of saidpipes (4,4′) comprises a proportional valve (5,5′), optionally with ahead loss device (5A).
 23. The facility according to claim 22, whereinthe proportional valve (5,5′) is of the butterfly valve type.
 24. Thefacility according to claim 20, wherein the ejector (3) comprises alongitudinal exit slot for the vapor, acting as a sonic throat,extending over the entire width of the substrate and a filtering mediumor a head loss member (3A) made of sintered material, preferably made oftitanium or in the form of a metal sieve with sintered stainless steelfibers, so as to equalize and rectify the velocity vectors of the vaporleaving the ejector (3).
 25. The facility according to claim 24,including means for adjusting the length of the slot to the width of thesubstrate.
 26. The facility according to claim 25, wherein said meanscomprise a means for rotating the ejector (3) around its supply pipe(4).
 27. The facility according to claim 20, wherein the ejector (3),the mixer (14), the pipes (4,4′), and the crucibles (11,12) arethermally isolated from the outside environment and heated by aradiation heater.
 28. The facility according to claim 20, includingoptional heating means for the vacuum enclosure (6).
 29. The facilityaccording to claim 21, wherein a first porous surface is arranged at theoutlet of the tubes (14A) and/or a second porous surface is arranged atthe outlet of the interstitial space (14B), so as to balance thepressures of the two respective vapors.
 30. The facility according toclaim 20, wherein the substrate (7) is a continuously moving metalstrip.
 31. The facility according to claim 20, allowing to directlydeposit on the substrate (7), by a vapor jet at sonic velocity, an alloyof the first metal M1 and of the second metal M2, wherein an additionalpipe (4″) is mounted in bypass on the supply pipe (4′) of the firstmetal M1 towards the mixer (14), having an isolating valve (5′) andleading to an additional ejector (3′) in the vacuum chamber (6), saidadditional ejector (3′) being configured to create a vapor jet of thefirst metal M1 at sonic velocity towards and perpendicular to thesurface of the substrate (7), the portion of the supply pipe (4′) of thefirst metal M1 leading to the mixer (14) being provided with anadditional valve (5B) intended to isolate the first crucible (12) fromthe mixer (14).
 32. A method for depositing a metal alloy coating on asubstrate (7), preferably a metal strip in continuous motion, using thefacility according to claim 20, wherein: the flow velocity of each ofthe metal vapors is regulated at the inlet of the mixer (14) so thatsaid flow velocity of said vapors at the inlet of the mixer is lower bya factor of 10, preferably by a factor of 50, than sonic velocity; theconcentration of each metal is independently adjusted during the mixtureof the vapors to be deposited on the substrate (7).
 33. The methodaccording to claim 32, wherein the flow velocity is less than 100 m/s,preferably from 5 to 50 m/s.
 34. The method according to claim 32, forimplementing the facility for depositing under vacuum a metal alloycoating on a substrate (7), preferably a metal strip in continuousmotion, wherein, said additional valve (5B) being closed and saidisolating valve (5′) being open, the first metal M1 is successivelydeposited at the level of the additional ejector (3′) and the secondmetal M2 is deposited at level of the ejector (3) in the vacuum chamber(6) on the substrate (7).
 35. The method according to claim 32, forimplementing the facility for depositing under vacuum a metal alloycoating on a substrate (7), preferably a metal strip in continuousmotion, wherein, said additional valve (5B) being open and saidisolating valve (5′) being closed, the M1+M2 alloy is directly depositedon the substrate (7) at the level of the ejector (3) in the vacuumchamber (6).
 36. The method according to claim 32, for implementing thefacility for depositing under vacuum a metal alloy coating on asubstrate (7), preferably a metal strip in continuous motion, wherein,both the additional valve (5B) and the isolating valve (5′) being open,the first metal M1 is successively deposited on the substrate (7) at thelevel of the additional ejector (3′) and the M1+M2 alloy is directlydeposited at the level of the ejector (3) in the vacuum chamber (6). 37.The method according to claim 32, wherein the metal or alloydeposition(s) are followed by a thermal treatment.